although Tim's translation of Sowerby's description 'Blanc-de-Lait' sounds as though it should be 'milk white', in fact in the flesh 'Blanc-de-Lait' doesn't have the appearance of 'milk glass' - that's a type of opaque glass unrelated to the discussion here, and dissimilar in appearance.
Quoting from Ray Slack .............. "On 1 May 1880 a new glass was announced and a report of that date in the
Pottery Gazette gave the following appraisal .............
"Amongst the latest novelties in glass is an article called Blanc-de-Lait ware by Sowerby etc. etc. " ........... so there seems no doubt that the factory were responsible for choosing this new name.
I think that if this were manufactured today, then yes, we might call it opalescent - but as we appear currently to have various interpretations about the use of the word opalescent, then IMHO we should stick with Sowerby's original Pottery Gazette description of Blanc-de-Lait to avoid confusion with other products.
Subsequent to the C19, and with the C20 obsession with the word opalescent - the whole world of 'Blanc-de-Lait' goes pear shaped - and quoting again from the
Pottery Gazette ............ "Three years have been spent in experiments on the opalescent product by Mr. Sowerby and his art workmen etc. etc."
and from here on in the word opalescent seems to become the vogue word for anything with a hint of the opal appearance.
To further complicate matters - and IMHO it appears that Simon Cottle makes an error when speaking of Sowerby products from that period - he writes in the Tyne & Wear Museums Service guide to the exhibition of Sowerby glass in 1986, and when speaking of Vitro Porcelain, says - "" The first colour,
Turquoise - made in imitation of the turquoise mineral - resembled the light bluishness of true Chinese porcelain and is almost as translucent. It was closely followed by a milky, semi-transparent glass, entitled
Opal. This term has often been used to describe Sowerby's
Blanc-de-Lait colour which was developed in 1880 and is a solid opaque white""
I feel sure that Cottle has confused himself over two separate products - Opal Vitro-Porcelain is opaque and was first Registered in 1877, and Blanc-de-Lait wasn't invented until 1880 and appears translucent as Tim's piece here - so in theory there shouldn't be confusion.
Sowerby's first invention in their range of Vitro-Porcelain was an opaque white which they called 'Opal', and this was first Registered with the Board of Trade in 1877 - though the actual pieces produced appear to have been designs that the company had Registered the previous year.
Sowerby's true 'Opal' Vitro-Porcelain' is opaque, and not a semi-transparent material as described by Cottle - this apparent use of the word Opal for the two products has given rise to some confusion between Blanc-de-Lait and Opal Vitro-Porcelain, particularly for people who haven't seen both products - either in a book or in the flesh.
In the aforementioned Tyne & Wear publication, Simon Cottle reproduces a photographic image of Sowerby's products, with the caption .... ""A group of opalescent press-moulded glass with amber staining, rose and green (or 'Vaseline'?), c. 1882."" The reference to vaseline i.e. u.v. reactive, seems difficult to understand as all eight pieces look to be Blanc-de-Lait and none has a green appearance. I could be wrong but don't think Sowerby did an opalescent uranium green - though of course they certainly produced uranium glass.
With the potential for confusion regarding some of Sowerby's C19 inventions i.e. Opal Vitro-Porcelain and the opalescent appearance of Blanc-de-Lait, I'd suggest that it will make for a clearer understanding of which product we're discussing if we retain the factory's original description of Blanc-de-Lait - for pieces such as Tim's - rather than just a blanket word opalescent.
Apologies this is over long - not easy when discussing antique matters.
